1. Field of the Invention
The present invention relates to an electro-photographic image forming apparatus. More particularly, the present invention relates to a developing unit having a photosensitive medium shutter that shields a photosensitive medium for reducing light fatigue of the photosensitive medium and an electro-photographic image forming apparatus having the same.
2. Description of the Related Art
Generally, an electro-photographic image forming apparatus is an image printing machine that prints an image after forming an electrostatic latent image by scanning light onto a photosensitive medium charged to a predetermined potential. The electrostatic latent image is developed and fixed on the photosensitive medium into a visible image by applying a developing agent such as a toner, thereon.
FIG. 1 is a side view illustrating a conventional developing unit mounted in an inner side of an electro-photographic image forming apparatus that can print a color image.
Referring to FIG. 1, a plurality of developing units 10C, 10M, 10M, and 10K for printing a color image can be vertically mounted in the electro-photographic image forming apparatus. Photosensitive media 15C, 15M, 15Y, and 15K, on which an electrostatic latent image is formed by light scanned from a light scanning unit (not shown), are mounted in the housings 12C, 12M, 12Y, and 12K of the developing units 10C, 10M, 10M, and 10K, respectively. One side of each of the photosensitive media 15C, 15M, 15Y, and 15K is opened to the outside of the housings 12C, 12M, 12Y, and 12K for printing the color image on printing papers. Also, developing agents, that is, toners, of cyan (C), magenta (M), yellow (Y), and black (B) colors for displaying the electrostatic latent images in cyan (C), magenta (M), yellow (Y), and black (K) colors are respectively filled in each of the housings 12C, 12M, 12Y, and 12K.
When the photosensitive media 15C, 15M, 15Y, and 15K are used for long hours, a light fatigue phenomenon, that is, reduced sensitivity to light, can occur. Then, the photosensitive media must be replaced since clear image printing is impossible. The light fatigue phenomenon may appear early if the photosensitive media are exposed to external bright light often and for long hours.
However, the four developing units 10C, 10M, 10M, and 10K depicted in FIG. 1 are disposed close to each other. Therefore, it is difficult to mount photosensitive medium shutters for shielding external light on each developing unit 10C, 10M, 10M, and 10K due to a narrow available inner space. It has been reported that some developing units have a photosensitive medium shutter that shields external light using a thin non-transparent film. However, the thin non-transparent film is not safe enough to protect the photosensitive media from an external impact, that is, there is a high risk of damaging the photosensitive media.
Accordingly, a need exists for an electro-photographic image forming apparatus having an improved developing unit that substantially prevents exposing the photosensitive medium to light.